/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.trino.sql.ir.optimizer.rule;

import com.google.common.collect.ImmutableList;
import io.trino.Session;
import io.trino.sql.ir.Expression;
import io.trino.sql.ir.Logical;
import io.trino.sql.ir.optimizer.IrOptimizerRule;
import io.trino.sql.planner.Symbol;

import java.util.List;
import java.util.Map;
import java.util.Optional;

/**
 * Flatten nested logical terms. E.g,
 * <ul>
 *     <li>{@code And(And(a, b), And(c, d), ...) -> And(a, b, c, d, ...)}
 *     <li>{@code Or(Or(a, b), Or(c, d), ...) -> Orr(a, b, c, d, ...)}
 * </ul>
 */
public class FlattenLogical
        implements IrOptimizerRule
{
    @Override
    public Optional<Expression> apply(Expression expression, Session session, Map<Symbol, Expression> bindings)
    {
        if (!(expression instanceof Logical logical)) {
            return Optional.empty();
        }

        if (logical.terms().stream().noneMatch(e -> e instanceof Logical inner && inner.operator() == logical.operator())) {
            return Optional.empty();
        }

        ImmutableList.Builder<Expression> terms = ImmutableList.builder();
        flatten(logical.operator(), logical.terms(), terms);
        return Optional.of(new Logical(logical.operator(), terms.build()));
    }

    private void flatten(Logical.Operator operator, List<Expression> terms, ImmutableList.Builder<Expression> accumulator)
    {
        for (Expression term : terms) {
            if (term instanceof Logical logical && logical.operator() == operator) {
                flatten(operator, logical.terms(), accumulator);
            }
            else {
                accumulator.add(term);
            }
        }
    }
}
